The present invention relates to a toner for use in an image forming method, such as electrophotography, electrostatic recording, magnetic recording and toner jetting, a process for producing the toner, and an image forming method using the toner.
Hitherto, a large number of electrophotographic processes have been known, inclusive of those disclosed in U.S. Pat. Nos. 2,297,691; 3,666,363; and 4,071,361. In these processes, in general, an electrostatic latent image is formed on a photosensitive member comprising a photoconductive material by various means, then the latent image is developed with a toner, and the resultant toner image is transferred via or without via an intermediate transfer member onto a transfer(-receiving) material such as paper etc., as desired, fixed by heating, pressing, or heating and pressing, or with solvent vapor to obtain a copy or print carrying a fixed toner image. A portion of the toner remaining on the photosensitive member without being transferred is cleaned by various means, and the above mentioned steps are repeated for a subsequent cycle of image formation.
An example of ordinary full-color image forming process will now be described. A photosensitive member (electrostatic image-bearing member) in the form of a drum is uniformly charged by a primary charger and then subjected to imagewise exposure with laser light modulated by a magenta image signal obtained from an original to form an electrostatic image on the photosensitive drum, which is then developed with a magenta toner contained in a magenta developing device to form a magenta toner image. Then, the magenta toner image formed on the photosensitive drum is transferred directly or indirectly onto a transfer material under the action of a transfer charger.
The photosensitive drum after the above-mentioned developing of an electrostatic image is charge-removed by a charge-removing charger and cleaned by a cleaning means so as to be prepared for a subsequent cyan-image forming cycle including charging again by the primary charger, a cyan toner image formation and a transfer of the cyan toner image onto the transfer material carrying the magenta toner image already transferred thereto, followed further by a yellow-image forming cycle and a black image forming cycle to provide the transfer material with four-color toner images thereon. Then, the transfer material carrying the four-color toner images is subjected to fixation under application of heat and pressure, thereby forming a full-color image.
In recent years, an image-forming apparatus performing an image forming method as described above not only is used as a business copier for simply reproducing an original but also has been used as a printer, typically a laser beam printer (LBP), for computer output, and a personal copier (PC) for individual users.
In addition to such uses as representatively satisfied by a laser beam printer, the application of the basic image forming mechanism to a plain paper facsimile apparatus is also popular.
Particularly, for such uses as a color printer for a personal computer and a personal color copier of which a rapid enlargement of market is being expected in future, a stronger desire is posed on such image forming apparatus, regarding a smaller size, a higher speed, a higher image quality and a higher reliability. Among all, a high reliability for maintaining the initial image quality in continuous image formation is strongly required, and for complying with such requirements, the improvement in chargeability is an essential subject of improved toner performance.
In either of the two-component development system wherein an amount of charge is determined by triboelectrification between a toner and a carrier, and a mono-component development system wherein an amount of charge is determined by triboelectrification between a toner on a developer-carrying member and a charge-imparting member, several problems have been left as objects of improvement regarding the charge amount, the charging speed and the maintenance of charge.
From a viewpoint of solving the above problems by controlling the toner shape, a suspension polymerization process has been proposed for producing a toner (JP-B 36-10231). In the suspension polymerization process, a monomer composition is prepared by uniformly mixing (i.e., dissolving or dispersing) a polymerizable monomer and a colorant, and optionally a polymerization initiator, a crosslinking agent, a charge control agent, and other additives, and the monomer composition is dispersed in an aqueous medium containing a dispersion stabilizer under the action of an appropriate stirrer, and subjected to polymerization, thereby providing toner particles having a desired particle size. Compared with the pulverization process, the suspension polymerization process allows easier control of particle size and its distribution and accordingly provides a toner having a narrower charge distribution and allowing easier charge control.
In the suspension polymerization system, a dispersion stabilizer used is attached to dispersed droplets, thereby uniformly stabilizing the dispersed droplets owing to its electrical polarity. It has been generally acknowledged that a toner chargeability is adversely affected if such an ionic or electrically polar substance has not been sufficiently removed therefrom.
As the dispersion stabilizer, there has been generally used a water-soluble polymer, such as polyvinyl alcohol or gelatin, or fine powder of hardly water-soluble inorganic substance, such as barium sulfate or calcium carbonate. However, the removal of such a dispersion stabilizer is generally difficult, and particularly a water-soluble polymer is difficult to remove because of high viscosity of its aqueous solution, thus being liable to remain in a large amount on the resultant toner particles and adversely affecting the triboelectric chargeability to result in remarkably inferior image qualities.
For solving these problems, JP-A 46-130762, JP-A 61-22354 and JP-A 2-148046 have proposed a process of using calcium phosphate as a dispersion stabilizer. More specifically, JP-A 2-148046 has proposed a process wherein calcium phosphate is dissolved in an acidic aqueous solution, a polymerizable monomer composition is dispersed in suspension under stirring, and an alkali hydroxide is added to again precipitate calcium phosphate on the droplets of the monomer composition for subsequent polymerization. JP-A 56-130762 and JP-A 61-22354 have proposed a process of using an adduct of sodium tertiary phosphate and calcium chloride as a dispersion stabilizer.
On the other hand, proposals of regulating the residual amount of dispersion stabilizers have been made, e.g., in JP-A 8-50370 and JP-A 8-160661. Based on a similar concept, the control of a residual amount of dispersion stabilizer in an emulsion dispersion process has been proposed in JP-A 9-218532. On the other hand, in contrast with such a general trend, JP-A 9-114125 has proposed to leave a certain amount or more of dispersion stabilizer.
Further, JP-A 1-217466 has proposed a toner production process wherein a monomer composition containing a polymerizable monomer and a copolymer of a water-soluble SO3X group-containing monomer and an oil-soluble monomer is subjected to suspension polymerization. JP-A 2000-56518 has proposed a toner comprising a copolymer of a vinyl monomer and an SO3X group-containing (meth)acrylamide. According to these proposals, some improvement in chargeability is recognizable. However, in view of Examples of these proposals, the dispersion stabilizer remaining in the product toner has not been substantially removed, so that problems regarding chargeability and developing performance attributable to the residual dispersion stabilizer have not been sufficiently solved.
Accordingly, a generic object of the present invention is to provide a toner capable of solving the above-mentioned problems.
A more specific object of the present invention is to provide a toner having good chargeability which is little affected by environmental changes.
Another object of the present invention is to provide a toner providing good image density which is little affected by environmental changes.
Another object of the present invention is to provide a toner capable of retaining good transferability even in continuous image formation.
Another object of the present invention is to provide a toner showing good fixability.
Further objects of the present invention are to provide a process for producing such a toner, and to provide an image forming method using such a toner.
According to the present invention, there is provided a toner comprising: toner particles each comprising at least a binder resin, a colorant, a release agent and a sulfur-containing polymer, and an external additive;
wherein the toner particles contain 100 to 30,000 ppm by weight thereof of at least one element selected from the group consisting of magnesium, calcium, barium, zinc, aluminum and phosphorus.
According to the present invention, there is also provided a process for producing a toner, comprising:
dispersing a monomer composition comprising at least a polymerizable monomer, a colorant, a release agent and a sulfur-containing polymer in an aqueous medium containing at least one element selected from the group consisting of magnesium, calcium, barium, zinc, aluminum and phosphorus, to form droplets of the monomer composition therein,
subjecting the droplets of the monomer composition to polymerization in the aqueous medium to form toner particles containing 100 to 30,000 ppm by weight thereof of at least one element selected from the group consisting of magnesium, calcium, barium, zinc, aluminum and phosphorus, and
blending the toner particles with an external additive to form a toner.
The present invention further provides an image forming method, comprising at least:
a charging step of charging an image-bearing member,
an electrostatic image forming step of forming an electrostatic image on the image-bearing member,
a developing step of developing the electrostatic image with the above-mentioned toner carried on a developer-carrying member to form a toner image on the image-bearing member,
a transfer step of transferring the toner image from the image bearing member to a transfer material via or without via an intermediate transfer member, and
a fixing step of fixing the toner image onto the transfer material.
These and other objects, features and advantages of the present invention will become more apparent upon a consideration of the following description of the preferred embodiments of the present invention taken in conjunction with the accompanying drawings.